Many different types of printing have been invented, a large number of which are presently in use. The known forms of printers have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and inkjet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of inkjet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on inkjet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Inkjet printers themselves come in many different types. The utilisation of a continuous stream ink in inkjet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electrostatic inkjet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of continuous inkjet printing including the step wherein the inkjet stream is modulated by a high frequency electrostatic field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezo-electric inkjet printers are also one form of commonly utilized inkjet printing device. Piezo-electric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezo-electric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezo-electric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezo-electric push mode actuation of the inkjet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a sheer mode type of piezo-electric transducer element.
Recently, thermal inkjet printing has become an extremely popular form of inkjet printing. The inkjet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclose inkjet printing techniques which rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
Most of these devices obviously involve the ejection of the fluid on demand. The ejection of the fluid requires a certain amount of energy depending upon the inkjet device utilized. Unfortunately, the utilization of a particular device will be under varying physical circumstances. For example, the density, specific heat capacity, viscosity, thermal conductivity and surface tension will vary with varying temperatures, sometimes by orders of magnitude. For example, there is a substantial variation in water viscosity with temperature. Where a water based ink is used it is likely that a similar response will be present in ink. Of course, with inks of varying compositions, different values will be relevant. The variation in these parameters can produce substantial fluctuations in the operation of an inkjet device. For example, substantial fluctuations can occur in the energy required to eject a single drop.